Acoustic Doppler Current Profilers (“ADCPs”) are used by oceanographers and other scientists and technicians to measure the velocity water in lakes, rivers, bays and oceans. ADCPs use acoustic beams to measure current velocities and provide profiles of velocity measurements over a series of depth cells. ADCPs operate by transmitting sound signals through acoustic transducers and receiving echoes back from particles in the water. The change in frequency of the sound being sent compared to that being received, called the Doppler shift, is analyzed to determine the velocity of the water. Commonly used frequencies are in the range of under 100 kHz to about 5,000 kHz.
The acoustic frequency of an ADCP has a major impact on the performance of the system. More particularly, the ability to have an ADCP with multiple beam sets operating at different frequencies would provide better operational flexibility and achieve better results through a variety of measurement options and the ability to tune operation to different conditions. However, ADCPs typically are designed to operate at a single frequency. While some ADCPs have more recently been designed to operate at multiple frequencies, the frequency needs to be changed manually while the device is not in operation. Thus, there is a need for an ADCP that automatically adjusts operating frequencies of the sound signals being transmitted during operation and can operate at more than one frequency at the same time.
The processing method used by an ADCP to measure the Doppler shift is also important, and there are three common processing methods, each having different performance characteristics, advantages and disadvantages. Incoherent processing, or narrow band processing, can be used under a wide range of conditions to measure a wide range of velocity values. However, velocity data gathered by incoherent processing has a relatively high level of noise that requires the system to engage in a lot of averaging to remove. Pulse coherent processing has a much lower noise level than incoherent processing but has other limitations such as a lower measurable maximum velocity.
The third type of processing is called broadband processing, and is essentially a hybrid between incoherent and pulse coherent processing. Broadband processing provides a maximum velocity higher than pulse coherent but lower than incoherent with noise levels lower than incoherent but higher than coherent. These three processing methods, when used in combination, can achieve higher performance than is possible by using just one method. However, most existing ADCPs are capable of running only one of these processing methods at a time. Thus, there is a need for an ADCP that can run more than one processing method concurrently and automatically adjust the processing methods being used.
Another disadvantage of existing ADCP systems is that the subsystem for sending acoustic signals and receiving depth and velocity data (i.e., the collection loop) is typically separate from the subsystem that runs the processing method to analyze the received data. This type of arrangement can be inefficient and limit both the quantity and quality of data that can be collected. Thus, there is a need for an ADCP that runs the collection loop in parallel with the processing and analysis subsystem.
Therefore, there exists a need for an ADCP that can operate at different acoustic frequencies at the same time. There also is a need for an ADCP than can run more than one processing method concurrently. There exists a need for an ADCP that runs the collection loop and the processing in parallel. In particular, there is a need for an ADCP that can automatically change operating frequencies and processing methods such that it operates at different frequencies and employs different processing methods concurrently.